The use of chain extenders and curing agents for the preparation of polyurethanes and of hardeners for epoxy resins is well known in the art. Polyurethanes, for example, may be obtained by reacting compounds having H-reactive groups such as polyether polyols or polyester polyols with a diisocyanate to form a prepolymer which, in a second step, is then reacted with a curing agent to form the polyurethane. Epoxy resins, on the other hand, may be obtained by reacting epichlorohydrin with an alcohol or phenol to obtain a glycidyl derivative which then is reacted with a hardener to obtain the cured epoxy resin.
The structure of the curing agents and the reactivity of their functional groups are often used to modify the properties of the final product or to control the reaction rate of the polymer formation and the processability of the polymer.
Commonly used chain extenders and curing agents for the preparation of polyurethanes (PU) and epoxy resins are aromatic diamines such as alkyl-substituted and/or chlorinated phenylenediamines or 4,4′-methylene-bisanilines. In the preparation of polyurethanes, the amino groups of these diamines will react with isocyanato groups to give urea moieties. The effect of such compounds on the properties of the polymer system substantially depends on the nature and positions of the alkyl substituents and/or the number and/or positions of the chlorine atoms on the aromatic rings. Sterically hindered diamines such as 4,4′-methylenebis-(3-chloro-2,6-diethylaniline) (M-CDEA) and 4,4′-methylenebis-(2,6-diethylaniline) (M-DEA) are often used as a curing agent. These compounds, however, do not allow easy processing, as their melting point is relatively high. Other well known compounds, such as 4,4′-methylene-bis-(2-chloroaniline) (MOCA) or 3,5-bis(methylthio)toluenediamines (E-300) are toxic and/or malodorous.
It has been an object of the present invention to provide novel aromatic diamines having low toxicity and no offensive odor, combined with moderate reactivity resulting in a convenient gel time (or pot life) when mixed with the urethane prepolymers or epoxy resins. The diamines should also be liquid or semi-liquid at room temperature, or at least easily soluble in the (uncured) epoxy resins, isocyanates and diols used as starting materials in the production of cured epoxy resins and polyurethanes.